The constantly increasing operational speeds of digital computers are creating a demand for corresponding increases in the data storage capacities of magnetic tape recording and reproducing systems, while maintaining the special requirements of high speed digital tape systems.
Tape recording and reproducing systems for use as computer data storage devices are required to provide high data transfer rates and to perform a read check on all written data. To satisfy these requirements, conventional tape systems typically employ methods of recording known as linear recording, in which the tracks of data lie parallel to each other and to the edge of the tape, or helical scan recording, in which the tracks of data lie parallel to each other but diagonal to the edge of the tape. The linear recording method offers higher data transfer rates; however, it is desireable to obtain higher data densities while retaining the advantages of this method.
Tape track densities are limited by crosstalk, which occurs when reading is interfered with by data of adjacent tracks. Crosstalk is exacerbated by error in head gap alignments. Some methods have been implemented to minimize this effect, such as leaving guard bands between tracks, or using wider write head gaps. These methods, however, limit track densities.
A method of recording known as azimuth recording has been used in helical scan systems in order to decrease the effects of crosstalk and thus increase the track density of these systems. Azimuth recording results in a recorded track pattern in which the magnetization directions of adjacent data tracks lie at different azimuth angles to each other. This method greatly reduces intertrack crosstalk, allowing tracks to be placed closer together. The need for guard bands or wide write heads is thus reduced or eliminated. The helical scan method, however, is subject to limited data transfer rates.
U.S. Pat. No. 4,539,615 to Arai et al., Azimuthal Magnetic Recording and Reproducing Apparatus, 1985, discloses a number of heads, head assemblies, and methods which can be used to employ azimuth recording in linear tape systems. However, most of the magnetic heads contain multiple read and/or write head gaps which are not parallel to each other or to the sides of the head. Accordingly, these heads are more difficult to manufacture, and they are incapable of reading standard tapes recorded with no azimuth angle. Also, most of the magnetic heads available are not capable of performing a read check on newly written data. Those heads which are capable of performing a read check do so at the added cost of an extra column of head gaps.
Another problem which limits tape track densities is lateral tape motion, which is the random and unavoidable tendency for a tape to drift in a direction lateral to the direction of tape motion. During a tape write, lateral tape motion causes track directions to deviate from the parallel to the edge of the tape. During a read, lateral tape motion causes misregistration of the read head over the track being read. This misregistration results in read data error.
Servo tracking techniques have been developed to reduce the effects of tracking error and thus improve the data capacity of tape systems. Known servo techniques vary widely, but most involve methods of dynamically moving the read head gap to continually reposition it over the written data track. The movement of the read head gap compensates for lateral tape motion during a read. However, lateral tape motion during writing is not controlled with respect to the write head gap; thus, the distance between tracks is still limited to the magnitude of the lateral tape motion in order to avoid over-writing previously written tracks. Known servo techniques are also costly in that they may require the use of preformatted tapes or additional heads.
It is desireable to present a magnetic head with parallel head gaps which is relatively inexpensive and easy to manufacture, and which can be utilized to provide an azimuth recording pattern to decrease the effects of crosstalk, thus increasing track density, while maintaining the ability to read standard non-azimuth format tapes. It is also desireable to be able to perform a read check after write with this head. Further, it is desireable to present a low cost servo tracking mechanism which works in concert with this head to control the effects of tracking error during writing as well as during reading in order to further increase track density. It is then possible to provide a tape system suited for computer data applications in which the data capacities are greatly increased over those of the prior art.